1. Technical Field of the Invention
The present invention relates generally to an object recognition apparatus for vehicles equipped with a radar working to track and recognize an object such as leading vehicles, and more particularly to such an object recognition apparatus designed to detect the presence of any dirt which is adhered to the radar as an obstacle to emission of a radar wave or reception of a radar return.
2. Background Art
Japanese Patent First Publication No. 2002-22827 teaches an automotive object recognition apparatus equipped with a radar which works to emit radar waves such as laser beams over an angular range defined in front of a radar-installed vehicle and receive returns of the radar waves from an object to recognize the object. This type of apparatus is used in, for example, an automotive system designed to sound an alarm when the distance to a leading vehicle falls within a warning range or to control the speed of the radar-installed vehicle so as to keep the distance to the leading vehicle at a selected value.
Radars used in the above type of object recognition apparatus usually have a glass or resinous protective cover installed on a front surface of the radar through which radar waves are emitted in order to protect it from environmental conditions. Therefore, adhesion of dirt such as dust to the protective cover may result in error in transmission of laser light through the protective cover, thereby reducing the ability to track or recognize an object.
Installation of a light-sensitive element on an optical path on which a return of a radar wave reflected by the dirt travels is proposed to detect the adhesion of dirt to the protective cover. This proposal, however, encounters the drawback in that the adhesion of dirt such as sherbet ice or snow may cause the laser light to partly transmit through the dirt or scatter outside the dirt without reflection thereof to the light-sensitive element, thus resulting in an error in sensing the reflected laser light.